The invention relates to a device for receiving and handling core material, and more particularly, to a device which will facilitate the receipt of a columnar mass of core material from a core barrel for retaining the integrity thereof.
It is generally the practice when drilling oil and gas wells to recover whole vertical sections of prospective geological formations at various depths in the drilling operation. This routine sampling is called coring and aids in determining the geological characteristics of the sub-structure. Such steps have, since the inception of deep hole drilling, been integral to proper drilling rig operations in the ultimate analysis of a particular area for oil and gas content. Consequently, coring devices have been developed for recovering columnar masses of core material from deep in the earth. The core materials are then brought to the surface for examination.
Prior art coring apparatus has included specially designed cutting heads in the form of hollow drill bits affixed to the end of elongated structures called core barrels. Conventional barrels are generally comprised of stationary inner and rotatable outer sleeves. The outer sleeves rotate with the drill pipe and rotate the drill bit. As the formation is penetrated, the "core" is fed into the inner sleeve. When a sufficient core sample has been taken and/or the inner sleeve of the barrel is full, it is raised to the surface. The core sample may be as long as 60 feet and up to 4 inches in diameter to comprise a mass weighing half a ton.
The conventional core barrel, having been withdrawn from the well, is generally suspended in the derrick above the rig floor for removal of the core. A device commonly referred to as a "core catcher," affixed to the end of the barrel, prevents the core sample from dropping out during withdrawal and while suspended in the derrick. The core catcher and the outer sleeves are removed to provide access to the core sample contained within the inner sleeve. Attention is then directed to the process of receiving the core from the barrel. It is important to recover the core intact or in a logical, orderly fashion in order to retain the characteristics of the geological structure for analysis.
Certain prior art methods and apparatus for recovering the core sample from the vertically suspended barrel include antiquated hand operated devices and less than optimal manual techniques. For example, on most conventional drilling rigs or platforms, a set of tongs is attached to the core barrel for gripping the exposed core therein. The core barrel is rested on the derrick floor. A core engineer operates the tongs and manipulates them to allow the core to controllably slide out of the barrel as it is slowly raised. With such a technique, only one to two feet are allowed to slide out at a time. The exposed length is then separated from the barrel by a rig hand who delivers a side blow to the columnar mass to break it off. This process is continued until all of the core has been recovered.
Numerous disadvantages are associated with the manual process of core recovery described above. If the core sample is well consolidated and not broken or fractured, this process may continue without incident. However, oftentimes, sections of the columnar sample are loose and/or mushy. Unconsolidated or broken sections may unexpectedly crumble off onto the rig floor. When this happens and the core cannot be retained with the tongs, the weight of the remaining core section may cause it to spew out of the barrel creating a useless and oftentimes dangerous pile of soil and rock. The core sample that is broken or crushed loses its primary value as well as causing a safety hazard on the usually wet and cramped rig floor.
It has been shown to be desirable to obtain the core sample in its entirety, and certain prior art drilling apparatus designs have been addressed to this problem. Specially designed core barrels have been made available which include means for encapsulating the core in either plastic or rubber sleeves as it is collected in the well. This approach alleviates many of the problems of recovery discussed above. However, such an apparatus, besides being more expensive than the conventional core barrel, is subject to damage by certain drilling fluids at commonly encountered elevated down hole temperatures. Moreover, usually only 20 feet of core, at generally only a 3 inch diameter, can be taken from the well at any one time, necessitating more "round trips" for a predetermined core section length.
Certain other prior art core recovery devices include means for removing the core material from the well in the exact conditions encountered inside the earth, including the pressure which existed in the area where the core was taken. Such a device is described and claimed in U.S. Pat. No. 2,248,910 issued to D. W. Auld et al on July 8, 1941. It may be readily ascertained from the efforts to develop such core recovery devices that the recovery of the core sample in its uncontaminated entirety is very important to the oil and gas industry.
It would be an advantage therefore to avoid the problems of prior art core recovery methods and apparatus by providing a device that may be attached to the outlet end of a conventional core barrel to receive the core sample in its entirety. The invention of the present core receiver is constructed just for such a purpose. The recovery technique provided therewith is much more efficient than that of the method of manually handling core sections and less expensive than the utilization of specially designed core barrels. Additionally, the conventional core barrel may be used without the usual problems of contamination and possible loss of the integrity of the core sample.